Outwardly serene, his emotions boiled.

His sudden reaction surprised everyone, as he was always so outwardly charming.

Overt: Can be outwardly seen/ sensed by an observer.

seemingly, outwardly, ostensibly

You do this by outwardly showing your emotions.

This metaphor suggests that the person's facial expression was tense, turbulent, and troubled, causing you to feel concerned or uneasy. It conveys the idea of inner turmoil or distress being reflected outwardly through their appearance.